The overall objective of this research is a better understanding of the mechanisms involved in intestinal calcium transport in physiological, altered physiological and disease states. In order to accomplish this objective, experiments will be undertaken in animals, as well as in humans. In particular, animal experiments will be directed towards determining the role of intestinal calcium binding protein, brush border alkaline phosphatase and a basal/lateral membrane adenosine triphosphatase (ATPase), as they relate to vitamin D metabolism, hormonal relationships and intracellular calcium transport. Measurements in animals will include in vivo and in vitro calcium absorption, calcium binding activity, alkaline phosphatase and ATPase activity, chromatography of vitamin D metabolites, uptake of calcium by intestinal brush border and mitochondrial preparations and electronmicroscopy. Experiments in humans will include determination of calcium absorption and endogenous fecal calcium loss, using a combined balance isotope study and in vitro measures of transport and enzyme activity, using perorally obtained duodenal biopsies from patients with digestive disease disorders.